|Publication number||US7722304 B2|
|Application number||US 12/189,901|
|Publication date||May 25, 2010|
|Filing date||Aug 12, 2008|
|Priority date||Aug 13, 2007|
|Also published as||US20090047093|
|Publication number||12189901, 189901, US 7722304 B2, US 7722304B2, US-B2-7722304, US7722304 B2, US7722304B2|
|Original Assignee||Research Engineering & Manufacturing Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (13), Classifications (5), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of Provisional Application No. 60/955,479, filed on Aug. 13, 2007.
1. Field of the Invention
This invention relates to a thread locking/prevailing torque fastener assembly and especially to a fastener with an improved external thread profile geometry that optimizes assembly joint integrity.
2. Background Information
In general, it is accepted that the object of having a specially designed external thread on a fastener of the thread-locking type is to create a condition of mating thread interference when the fastener is screwed into a nut anchor that has been pre-tapped in accordance with a known and accepted thread standard such as the I.S.O. standard 965/1. The term “nut anchor” as used herein is meant to include any separate nut or any anchor or support into which the fastener may be threaded.
Such mating thread interference may occur at the thread major or outer diameter as shown in
Mating thread interference may also occur at the thread minor or inner diameter shown in
A third type of mating thread interference is depicted in
It is apparent that all of the above known assemblies rely only on mating thread interference to achieve the thread locking effect. It is generally accepted in the industry that the magnitude of the mating thread interference is the governing factor behind the degree of thread locking that can be obtained by any one of the above assemblies. In all of these examples, continued re-use of the threaded fastener causes wear of the mating threads, resulting in a lesser degree of thread locking over time.
While each of the prior thread interference assemblies just described can be effective in particular applications, there are some applications where they do not achieve the desired thread locking effect, with the result that assembly joint integrity may suffer. In other words, the threaded fastener may become loosened when the jointed assembly is subjected to externally applied forces. By the term “jointed assembly” is meant an assembly wherein the threaded fastener has been subjected to a tensile force that is induced in the fastener from the applied torque used to produce an acceptable assembly.
Accordingly, the present invention aims to provide an improved thread locking-type fastener assembly which produces superior assembly joint integrity when subjected to externally applied forces.
A further object of the invention is to provide a thread locking fastener assembly which can be reused without significantly losing its locking capacity.
Another object of the invention is to provide an assembly of this type which can be used in a variety of different applications.
Still another object is to provide such a fastener assembly which has an enhanced clamp load retention capability.
Yet another object of the invention is to provide a thread locking fastener which, when assembled to a nut anchor, provides one or more of the above advantages.
A further object of the invention is to provide such a fastener which is relatively easy and inexpensive to make in quantity.
Still another object of the invention is to provide a fastener of this type whose shank can have a cylindrical or lobular configuration.
Other objects will, in part, be obvious and will, in part, appear hereinafter.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.
In general, my invention uses the thread interference developed at the major or outer diameters of mating fastener and nut anchor threads to enhance overall thread locking performance by including a specially designed addendum on the fastener thread to store residual energy in the thread created by deflection of the addendum when the fastener is tightened in the nut anchor to effect an assembly.
As will be described in more detail later, the utilization of the residual or stored energy in the fastener thread is best utilized when the deflection of the thread addendum does not exceed that which would cause a permanent deformation of the fastener thread addendum. That is, the deflection is best kept within the “limit of proportionality” of the fastener thread material and geometry.
In accordance with the invention, the fastener has a threaded shank with an axial core and a helical thread formed on the core. The axial cross-sectional profile of the thread provides a radially inner thread base zone extending from the core to an imaginary datum line spaced from and parallel to the core axis. The profile also provides a radially outer thread addendum which extends from the datum line to the tip of the thread and which is deflectable. The thread base and addendum are bounded by leading and trailing faces extending from the core to the tip. The trailing face has a radially inner portion and a radially outer portion which join at the datum line so as to define an included angle less than 180° so that when the fastener is threaded into a nut anchor and the trailing face of the fastener thread is drawn against the leading face of the nut anchor thread with a selected force, the thread addendum is deflected so as to increase the included angle thereby storing residual energy in the fastener thread, resulting in a jointed assembly with enhanced joint integrity and clamp load retention.
For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:
Shank 24 includes a core 26 having a thread 28 generated on a helical form around core 26. This thread, which in axial section has a profile 28′, may extend the entire length of the core or along a portion thereof. The thread has a major or outer diameter 32, a minor or inner diameter 34 and a thread profile height 36 that is usually constant for a given size fastener. The magnitude of the helix or spiral angle α of the thread is determined by direct relationships between the outer diameter 34 and the thread's axial pitch 38. Usually, the axial pitch will be in accordance with that of the pre-tapped thread in the nut anchor chosen by the assembly fabricator.
Refer now to
As seen from
Above the datum line D, the addendum 42 is non-symmetrical about line L and it has a leading face portion 46 b and a trailing face portion 48 b. The face portion 48 b intersects face portion 48 a at a critical point 52 on datum line D and defines with the latter an included angle γ in the range of 158° to 162°, preferably 160°. The leading face portion 46 b may be more or less an extension of portion 46 a as shown by a broken line in
Refer now to
Referring now to
It should be noted that the base 40 of thread 28, being rigid, does not deflect to any appreciable extent. The axial force W applied at the critical point 52 in
Thus, it is the energy stored in the deflected addendum 42 that adds to and retains clamp load forces beyond those that can be developed using conventional thread locking assemblies such as those depicted in
As noted above, it is preferred that the leading face of the fastener thread 28 be notched. The preference for the notch is to ensure that when the thread addendum 42 is deflected as depicted in
The leading face portion 46 b of the thread addendum 42 need not be notched should the assembly design have no requirement for thread addendum deflection G to be established under forces that are below those of the tensile strength of the fastener 20.
Various modifications and additions can be made to my fastener without departing from the scope of the invention. For example, the leading and trailing portions of the thread profile 28′ can have a number of shapes designed to address particular purposes. Also, the pitch and size of thread profile 28′ may vary depending upon the material of nut anchor N. In addition, although the deflection of the thread addendum 42 is an integral part of the invention, it should not be assumed that the illustrations given by way of example cannot be modified in a way to achieve the above described clamp load retention to which the invention relates. Also, other design parameters can be based upon and varied in accordance with the materials of which the fastener and/or nut anchor are made.
It should be noted too that the present fastener may be made using the same processes used to manufacture other, more conventional fasteners of this general type that do not have the above described enhanced thread locking capability and at a similar cost. Therefore, it should have wide application.
It will thus be seen that the objects set forth above among those made apparent from the preceding description are efficiently attained. Also, various other changes may be made in the above construction without departing from the scope of the invention. Therefore, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all the generic and specific features of the invention described herein.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US1250748 *||Dec 21, 1916||Dec 18, 1917||Irving C Woodward||Self-locking screw-thread.|
|US3426820 *||Oct 5, 1967||Feb 11, 1969||Res Eng & Mfg||High friction screw|
|US3523565||Apr 29, 1968||Aug 11, 1970||Allied Prod Corp||Self locking male threaded fastener|
|US3882917 *||Apr 14, 1972||May 13, 1975||Litton Industrial Products||Self-locking thread|
|US3901066 *||May 20, 1974||Aug 26, 1975||Litton Industrial Products||Dies for making self-locking screws|
|US3927503 *||Dec 26, 1973||Dec 23, 1975||Standard Pressed Steel Co||Prevailing torque fastener|
|US4252168 *||May 16, 1979||Feb 24, 1981||The Lamson & Sessions Co.||Thread convolution|
|US4820098 *||May 3, 1985||Apr 11, 1989||Friedr. Boesner Gmbh||Screw|
|US5000638 *||Dec 21, 1989||Mar 19, 1991||Conti Fasteners Ag||Screw for contaminated pre-tapped holes|
|US5738472||Oct 17, 1996||Apr 14, 1998||Honeybee Robotics Inc.||Modified locking thread form for fastener|
|JP2006057801A||Title not available|
|JPS5919712A||Title not available|
|WO1989011044A1||May 1, 1989||Nov 16, 1989||Takuya Mikajiri||Locking screw|
|U.S. Classification||411/308, 411/312|
|Aug 12, 2008||AS||Assignment|
Owner name: RESEARCH ENGINEERING & MANUFACTURING INC.,RHODE IS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:PRITCHARD, ALAN;REEL/FRAME:021372/0225
Effective date: 20080811
|Nov 25, 2013||FPAY||Fee payment|
Year of fee payment: 4